1. Field of the Invention
The present invention relates to a lamp body control system for changing the illuminating direction of lamp bodies according to a steering angle of a vehicle.
2. Description of the Related Art
There has been known a conventional lamp body control system for changing the illuminating direction of lamp bodies equipped on a vehicle according to a steering angle of a vehicle. This lamp body control system is characterized in that a road surface in the traveling direction of the vehicle can be illuminated when the vehicle is running on a curved track. It is a common practice to use an encoder for outputting a pulse corresponding to a turning angle which utilizes an optical sensor or a magnetic sensor as a steering angle sensor for the lamp body control system. Some encoders output a relative angle whereas others output an absolute angle, and either of them are selected for use as required.
In the event that an encoder is used which can detect a relative angle, since a reference position first needs to be detected in implementing the control, an operation such as disclosed in JP-B-2-29539 has been required in which the illuminating direction of lamp bodies is fixed to a direction facing the front of a vehicle until a reference position for a relative angle is detected. In this method, however, since the illuminating direction of the lamp bodies is fixed to the direction facing the front of the vehicle in a condition resulting immediately after the control is initiated in which the reference position for the relative angle has not yet been detected, there is caused a problem that the illuminating direction of the lamp bodies cannot be controlled as in a case where the vehicle is started from a parallel parked condition in which it is parked between vehicles which are parked longitudinally relative to the curb of a road. In addition, there is known a technology such as disclosed in JP-B-6-104432 in which a steering angle when the ignition switch is turned off is stored, and then the control is initiated based on the stored steering angle when the ignition switch is turned on. In this method, however, there is caused another problem that in the event that the steering wheel is operated when the ignition switch is turned off, there is caused a deviation between an actual steering angle and the stored one.
While these problems can be solved by a method in which an absolute angle sensor is used or a method in which an encoder and a computing circuit are energized at all times, in general sensors for detecting an absolute angle are expensive, and a neutral position (or a reference position) needs to be calibrated at least once after a vehicle is produced, these causing a problem that the production costs are increased.
In addition, while a steering angle can be retained and updated by energizing the encoder and the computing circuit at all times, power is consumed at all times and therefore this triggers another problem that the battery goes flat. In addition, there is caused a risk that the reference value is deviated due to disturbances such as erroneous counting and noise.
The invention was made in view of the situations, and an object thereof is to provide a lamp body control system which utilizes an inexpensive relative angle sensor such as an encoder and which can change the illuminating direction of lamp bodies according to a steering angle immediately after the ignition switch is turned on whereas it consumes no current while the ignition switch is off.
With a view to attaining the object, according to a first aspect of the invention, there is provided a lamp body control system including a steering angle sensor (for example, a steering angle sensor 2 in an embodiment) for detecting a steering angle, a light emitting unit (for example, a lamp body 1 in the embodiment) which can change the illuminating direction thereof at least laterally, a driving unit (a lamp body driving unit 5 in the embodiment) for changing the illuminating direction of the light emitting unit, a control unit (for example, a control unit 6 in the embodiment) for controlling the driving unit based on an output from the steering angle sensor, and a straight ahead driving condition determining unit (for example, a step S13 in the embodiment) for determining the straight ahead driving condition of a vehicle, the lamp body control system being characterized in that the control unit directs the illuminating direction of the light emitting unit to a direction according to a steering direction and a variation in the steering angle in the event that the variation in the steering angle is larger than a predetermined value (for example, steps S3, S11 in the embodiment), whereas in the event that the variation in the steering angle is equal to or smaller than the predetermined value, the control unit return the illuminating direction toward a direction facing the front of the vehicle at a predetermined returning speed (for example, steps S3 to S10 in the embodiment) until the straight ahead driving condition determining unit determines that the vehicle is in a straight ahead driving condition after an ignition switch is turned on.
According to the construction of the first aspect of the invention, since the control unit is constructed to direct the illuminating direction of the light emitting unit to a direction according to a steering direction and a variation in the steering angle in the event that the variation in the steering angle is larger than a predetermined value, whereas in the event that the variation in the steering angle is equal to or smaller than the predetermined value, the control unit returns the illuminating direction toward a direction facing the front of the vehicle at a predetermined returning speed during a period of time from an ignition switch is turned on until the straight ahead driving condition determining unit determines that the vehicle is in a straight ahead driving condition, even in a case where an inexpensive relative angle sensor such as an encoder is used, the illuminating direction can be changed as the vehicle is steered immediately after the ignition switch is turned on. In addition, since there is no need to supply power to the encoder and a computing circuit at all times, there can be provided an advantage that no power is allowed to be consumed when the ignition switch is off.
According to a second aspect of the invention, there is provided a lamp body control system as set forth in the first aspect of the invention, wherein the system further comprises a vehicle speed sensor (for example, a right driven wheel speed sensor 3 or a left driven wheel speed sensor 4 in the embodiment), whereby the returning speed is changed according to a vehicle speed (for example, steps S5, S6, S7 in the embodiment).
According to the construction of the second aspect of the invention, since the vehicle speed sensor is provided, whereby the returning speed is changed according to a vehicle speed, an illuminating direction control can be implemented according to a change in the gazing properties of a driver in conjunction with a change in vehicle speed. In general, since the line of sight of the driver is directed to the front of the vehicle in many cases and the variation in line of sight to lateral directions decreases when the vehicle speed is high, it is effective that the illuminating direction is returned to the direction facing the front of the vehicle at a fast returning speed. In contrast, since the line of sight of the driver is directed to a direction in which the vehicle is steered in many cases when the vehicle is at rest or runs at an extremely low speed as in a case where it is started from a rest, it is effective that the illuminating direction is returned to the direction facing the front of the vehicle at low returning speed.
According to a third aspect of the invention, there is provided a lamp body control system as set forth in the second aspect of the invention, wherein the returning speed when the vehicle speed is equal to or larger than a given value (for example, a compensation xcex941 in the embodiment) is larger than the returning speed when the vehicle speed is smaller than the given value (for example, a compensation xcex942 in the embodiment).
According to the construction of the third aspect of the invention, since the returning speed when the vehicle speed is equal to or larger than the given value is set to be larger than the returning speed when the vehicle speed is smaller than the given value, the control of illuminating direction according to a change in the gazing properties of the driver in conjunction with a change in vehicle speed can be implemented in an ensured fashion.
According to a fourth aspect of the invention, there is provided a lamp body control system as set forth in any of the first to third aspects of the invention, wherein the straight ahead driving condition determining unit determines that the vehicle is in a straight ahead driving condition in the event that a condition continues for a predetermined period of time (for example, steps S13, S15 in the embodiment) in which a difference in rotation between left and right driven wheels (for example, a difference in output between the right driven wheel sensor and the left driven wheel sensor in the embodiment) is equal to or smaller than a certain value.
According to the construction of the fourth aspect of the invention, since the straight ahead driving condition determining unit is constructed so as to determine that the vehicle is in a straight ahead driving condition in the event that a condition continues for a predetermined period of time in which a difference in rotation between left and right driven wheels is equal to or smaller than a certain value, there is provided an advantage that the straight ahead driving condition can be determined in easy and ensured fashions. In addition, with a vehicle equipped with an ABS, since the wheel speed sensors are normally equipped on the vehicle, there is provided an advantage that no additional sensor needs to be installed in the system.